Middle Permian paleo-ecological conditions and depositional processes in Iran and causes of large-test fusulinids extinction

In order to examine the effect of depositional environments on large-test fusulinids in Middle Permian deposits of Iran two stratigraphic sections in Shotori and Bagh-e Vang Mountains in Tabas Block located in east-central Iran and one stratigraphic section in Hambast Valley, Abadeh area situated in west-central Iran were studied. The possible cause of the few occurrences of large-test fusulinids in Middle Permian shallow water carbonates of the Shotori section was high temperature (more than 36° centigrade) of paleo sea indicating unfavorable condition for algal-symbiont large-test fusulinids life. There is no large-test fusulinid in Middle Permian deep-water limestones with cherty interbeds of Bagh-e Vang section. In Hambast Valley section, the Middle Permian shallow-water subtidal limestones of the middle and upper parts of the Unit 1 of Surmaq Formation contain abundant large-test fusulinids. No large-test fusulinid is recorded from the deep-water limestones with cherty interbeds of the Unit 2 of the Surmaq Formation. The presence of cherts in the Middle Permian of Iran in both Bagh-e Vang and Hambast valley sections are related with Middle Permian chert-event and eutrophication also reported in South China and North America which is adverse for the life of large-test fusulinids in oligotrophic shallow water environment. Considering the local disappearance of the large-test fusulinids in the three studied sections before the end-Guadalupian bio-event, it can be concluded that the climate change and the nutrient level input had major role in extinction of these organisms..